The fundamental causes of medical errors are cognitive, although the errors are not always the fault of the individual who makes them. From the perspective of cognitive science, medical errors occur in large part due to inadequate information processing in cognitive tasks. In order to prevent or greatly reduce medical errors, it is critical to understand the underlying cognitive mechanisms that cause medical errors and how a person?s work environment contributes to and even induces those errors. The objective of this three-year project is to develop a cognitive framework of medical errors that includes a cognitive taxonomy, a cognitive theory, and a set of intervention strategies. We will achieve the following specific aims: First, we will systematically collect medical error data from published reports, public databases, and from our own observations in critical care settings by ethnographical and other naturalistic methodologies. We will focus on errors in medical decision-making, reasoning, and problem-solving tasks. Second, based on the data collected, we will develop a cognitive taxonomy that associates each type of medical error to a specific underlying cognitive mechanism. Third, we will develop a cognitive theory that explains why and predicts when and where a specific error occurs. Fourth, based on the cognitive taxonomy and the cognitive theory, we will develop a cognitive intervention strategy for each type of error in the taxonomy. These cognitive intervention strategies will be able to prevent or greatly reduce medical errors in a systematic way and on a large scale.